1. Field
This disclosure relates to a negative electrode for a secondary lithium battery and a secondary lithium battery including the same.
2. Description of the Related Technology
A secondary lithium battery is an energy storage device including a lithium metal oxide positive active material and a carbon-based negative active material and expressing a capacity though a redox reaction of intercalating and deintercalating lithium ions to and from the positive active material and the negative active material. The secondary lithium battery is generally used for an energy source of a small electronic device such as a mobile phone and a laptop computer, and has been developed to have enhanced energy density.
However, the demands for high input required fields such as an elevator, an automobile, and the high power required fields such as machine tools, hybrid electric vehicles (HEV), and electric vehicles (EV) have been increasing, so research on developing a battery having high input power has been undertaken.
The conventional energy storage device having high input power is an electrochemical capacitor (electrical capacitor). The electrochemical capacitor stores charges through adsorption and desorption of charges in a bilayer formed at an interface of between an electrode and an electrolyte by static electricity gravitation, different from the charge storage mechanism (redox reaction) of a secondary lithium battery.
Accordingly, the electrochemical capacitor has a merit of higher input power but has a drawback of lower energy density compared to the secondary lithium battery. Due to the low energy density, the electrochemical capacitor has limits in application to the various fields.
In order to overcome the limit of low energy density, development of a hybrid capacitor in which one electrode includes an electrode material for a secondary lithium battery has been attempted.
On the other hand, research on a secondary lithium battery has been performed using active carbon as an electrochemical capacitor for an electrode to enhance the input power characteristics.
When the active carbon is added to the positive electrode, the active carbon is disposed to surround the positive active material. An electrical bilayer is formed on the interface of the active carbon by applying a potential, and then it may store charges through adsorbing and desorbing ions to provide the high input power characteristics.
In addition, since the active material is a porous material, the electrolyte solution impregnates the material well, thereby minimizing the transferring distance of ions and improving the high input power characteristics.
When the active carbon is added to the negative electrode, an electrical bilayer is formed on the interface between the negative electrode and the electrolyte during the first charge, so it may store charges through the adsorption and desorption.
When the potential is further decreased, the large surface area of active carbon causes a side reaction between the active carbon and the electrolyte. As a result, an SEI (Solid Electrolyte Interface) is formed on the surface of the active carbon causing resistance.
Thus the intercalated lithium ions are not deintercalated and remain during the discharge. Accordingly, there is an increased necessity to develop a material that minimizes the irreversible reaction in the negative electrode and to improve the high input power characteristics through minimizing the transmitting distance and the adsorption and desorption of ions.